The present invention aims to define a number of requirements, including PRL material characteristics, for a floating PRL design which preserves eye dynamics. Such a floating PRL design solves the problems of cataract induction and iris pigment dispersion caused by the implantation of a PRL.
There are a number of patents describing the posterior chamber PRL concept and specific lens designs. U.S. Pat. No. 4,585,456, Blackmore, issued Apr. 29, 1986, discloses a phakic intraocular lens (IOL) composed of flexible materials which is positioned against the natural lens of the eye and is held in place immediately adjacent to.the natural lens and the ciliary sulcus. There are no specific disclosures of the PRL material properties, such as softness. The lens does not float in the eye but, rather, is fastened in place.
Other patents describe different ways of reducing IOP elevation and avoiding cataract formation by PRL designs and their fixation mechanisms. For example, Fedorov, in U.S. Pat. No. 5,480,428, issued Jan. 2, 1996, discloses a novel phakic lens design which has an opening through the center of the optic body. This open hole allows aqueous humor to flow through the lens body, thereby preventing IOP elevation, but it reduces the optical performance of the phakic lens. This patent also does not disclose the lens material properties or lens surface properties for such lens designs. Fedorov, in U.S. Pat. No. 5,258,025, issued Nov. 2, 1993, discloses that post-operative inflammation, caused by the contacting of the supporting elements with the ocular tissue, is prevented by moving supporting elements to the periphery of the phakic lens. The Zinn""s zonules are strong enough to hold the supporting elements in place without causing inflammation. Again, Fedorov failed to specify the lens material properties and lens surface properties. Further, this is not a floating lens design.
Finally, PCT Published Application WO 98/17205, Valunin et al., published Apr. 30, 1998, describes the structure of a phakic IOL, which floats in the eye. Valunin taught that the phakic IOL can be made from, for example, silicone, silicone-methacrylate copolymers, poly(methyl methacrylate), poly(hydroxyethyl methacrylate) and collagen/acrylate blends. However, no specific properties of a suitable material, such as mass per unit area or specific gravity, are defined.
Accordingly, there is a great need to identify desirable lens materials with required properties which, in combination with proper lens specifications, can preserve the eye dynamics after PRL implantation. The combination of lens design and the lens material properties makes it possible to avoid cataract induction and iris pigment dispersion. Neither the lens design alone nor the lens material properties alone can achieve the desirable floating features.
The object of the current invention is to provide a PRL, with a proper lens design and material properties, that may be placed in the posterior chamber of the human eye for correction of refractive errors. It is also the object of this invention to provide a PRL that can float in aqueous humor and that is very flexible and soft. The floating action and soft nature of the PRL will preserve the eye dynamics so that cataract induction of the human crystalline lens will be avoided and iris pigment dispersion eliminated. It is further an object of the present invention that this floating design and these benefits be achieved by selecting biocompatible materials having defined properties and by selecting other parameters, such as low mass per unit surface area (grams/mm2), of the PRL. It is a still further object of this invention that, due to the softness of the PRL material and the floating nature of the PRL design, when the iris contracts, it can move freely and constantly over the anterior surface of the PRL without causing iris pigment dispersion.
These and other objects are accomplished by a phakic refractive lens for implantation in the posterior chamber of the eye, said lens having no permanent fixation in the posterior chamber other than simple floating in the aqueous humor when positioned between the iris and the natural crystalline lens, said lens having the following properties:
(a) mass per unit surface area of from about 0.03 to about 0.30 mg/mm2, preferably from about 0.05 to about 0.13 mg/mm2;
(b) specific gravity of the materials used for said lens of from about 0.9 to about 1.2 grams/cm3; and
(c) the lens must be flexible, preferably the hardness of the material used for said lens being from about 20 to about 50 Shore A.
The present invention also encompasses a method for correcting the vision of a myopic or hyperopic patient comprising implanting a phakic refractive lens in the eye of said patient, said lens floating in the aqueous humor between the patient""s iris and natural lens with no permanent point of fixation, said phakic refractive lens having the following properties:
(a) the mass per unit area of the lens if from about 0.03 to about 0.30 mg/mm2;
(b) the lens is flexible; and
(c) the specific gravity of the materials comprising the lens is from about 0.9 to about 1.2 g/cm3.